/Engine/Source/Runtime/GeometryCore/Public/Util/IndexUtil.h
Find ordered edge [VertexID1,VertexID2] in TriangleVerts
index in range 0-2, or InvalidID if not found
namespace IndexUtil { template<typename T, typename Vec> int IndexUtil::FindTriOrderedEdge ( T VertexID1, T VertexID2, const Vec & TriangleVerts ) }